The invention relates to a spray coating device for a coating powder containing a powder duct, an electrode support mounted in the downstream end zone of the powder duct, an electrically insulating, integral tubular segment constituting a segment of the powder duct, and an electric contactor for setting up contact between a high-voltage conductor and an electric connecting line running through the electrode support to at least one high-voltage electrode supported by the electrode support.
A spray coating device of this kind is known from the European patent document 0 383 030 B1. It contains an electrode support fitted with a centering ring which is only about 3 mm long and which is inserted from the front into the downstream end of a powder duct of the spray coating device for the purpose of centering the electrode support.
To prevent electromagnetic fields or forces in the powder duct of the spray coating device from adversely acting on powder movement and spray coating, the high-voltage space between a high-voltage generator and at least one high-voltage electrode must be well screened from the electrode in order that only the electrode shall electrostatically charge the coating powder. Moreover leakage currents between the high-voltage conductive path and other components, for instance the powder duct, are unwanted because entailing loss of energy and moreover because they might lead to undesirably electrostatically charging the powder particles in the powder duct, in turn resulting possibly in powder deposits in the powder duct and in special cases in powder dust xe2x80x9cmigratingxe2x80x9d along the path of the leakage current. The larger the thickness of the electrically insulating material between the high-voltage conducting parts and the powder duct, the better the electrical insulation. However increasing the thickness of such an insulator conflicts with minimizing the bulk of the spray coating device and its weight.
The objective of the invention is to solve the problem of averting electric leakage currents and undesired electromagnetic fields between the high-voltage conducting parts and the coating powder in the powder duct of the spray coating device without entailing a bulkier and/or heavier spray coating device.
The above and other objectives of the present invention is achieved by setting the axial distance between the electric contactor and the rear end of the rear tubular segment to be at least 1.5 cm. Preferably, the axial distance is less than or equal to 4 cm. More preferably, the axial distance is in the range of from 2 to 3 cm.
In accordance with an aspect of the present invention, a channel is formed in a rearward-pointing offset of the tubular segment to annularly enclose, while being radially spaced from, the powder duct. The channel communicates on one hand with a compressed-air duct and on the other hand with an air duct running through the electrode support for feeding compressed air to the electrode.